Depending on what motor the tractor has, it sounds like it might need the valves adjusted. If it is an OHV Briggs this is more than likely the problem. If not ask again with more detail about your engine model.
you have a dirty battery post
The battery is dead - you would need to boost the vehicle in order for it to start , but once you shut the vehicle off it will not start again without boosting or hooking it up to a battery charger
Typically a charger is not meant ot "jump start" and engine. It provides a slow, regulated charge to the battery. A car battery or fully charged battery will typically provide enough pwoer to jump start your tractor. I recommend charging your battery for a number of hours (or overnight) till completely recharged. If the tractor will no start without a jump, your battery may be in need of replacement.
is the battery dead? if not check your connections and/or for corrosion
battery is low. get a boost or charge the battery.
Probably a weak battery
The tractor may not start because there may be a problem with the battery. You also need to make sure you have enough gas.
Go to a locksmith! Of course
Try getting a boost.....that'll help
Weak car battery
How is your battery ? Try a battery charger , battery jumpstarter pack , or a battery boost and see if it starts . ( also, it could be a battery cable connection )
When you open the hood , does the underhood light come on ? Or , if the drivers door is open with the key in the ignition do you hear the warning chime sounding ? If not , it sounds like a poor battery cable connection or a dead battery ( you could have a dead cell in the battery , in which case you can boost the battery to start the car , but if you shut it off it will not restart unless you boost the battery again )